It is known that fluorine can be exchanged for chlorine, bromine or iodine bonded to phosphorus by reaction of the halophosphorus compound with a metal fluoride. The transhalogenation reaction is quite slow and difficult to push to completion. It is sometimes desirable to replace chlorine, bromine, or iodine bonded to phosphorus with a fluorine atom. For example, Burton U.S. Ser. No. 020,023 filed Feb. 27, 1987 describes a family of hydrocarbylfluorophosphites that are very effective stabilizers in polyolefins, especially in combination with phenolic antioxidants, and are also hydrolytically stable. These compounds are made by first forming a hydrocarbyl chlorophosphite by reaction of an appropriate aliphatic or aromatic hydroxy compound with PCl.sub.3 to form a mono or dichlorophosphite and then transhalogenating the chlorine atom with fluorine by reaction with a metal fluoride such as potassium fluoride. In view of the exceptional properties of these fluorophosphites, a need exists for an improved synthetic method.